Typically, a complete process for developing a new product from design, making a prototype, management of production processes, mass production to introducing the product to the market, there always need a prototype for evaluation and examination. Thus, a prototype that is easily manufactured and amended is an important factor for a successful product. How to manufacture the prototype that meets needs is crucial for not spending too much manufacturing cost.
There are numerous methods available for prototype production such as the conventional manual production, CNC milling and carving machine. As for the conventional manual model production, except for experiences, it lacks precision. The CNC milling or carving machine are also confined to the types of chucks, bits or the size of the machine.
With the improvement in technologies, the quick growth of CAD package software has distinguishably shortened the development cycle for new products. For the past few years, the industry of Rapid Prototyping has well integrated with the CAD and production technologies and remarkably improves the efficiency for product design. The methods of quick formation can be classified as Layer Manufacturing, Automated Fabrication, Freeform Fabrication and Solid Imaging, etc. For the continuous development of past decades, there are ten more types of RP models available in the current markets. The methods of rapid formation can, according to the use of energy resources, be classified as Light Illuminating Processing, Stick-Formation processing and Complex Formation Processing. According to the documentary records, we classify the production process for rapid prototype making in terms of work piece properties, energy resources types, and stacking types. As shown in FIG. 1, some conventional production processes are as follows:
1. SLA (Radiation Hardening Formation): It is currently the most widely applied processing method with the formation by means of Stereolithography Formation. This production process is designed with He—Cd or Ar+ ultraviolet laser galvanometer-mirror to scan and illuminate the fluid polymers (light hardening resins). The resin required for formation becomes a thin film (around 0.15 mm˜0.05 mm). Then, with the descending of Z-axis, the work piece zone is coated with a layer of liquid polymers. By using a scraper to destroy the surface tension of the liquid polymers a flat surface is obtained. The liquid polymer is then scanned by laser beams so that the layers are combined firmly. A 3-D solid work piece is obtained by repeating the previous steps. The flow chart of SLA (Radiation Hardening Formation) is shown in FIG. 2.
A U.S. Patent owned by 3D Systems, USA, filed on Aug. 8, 1984, issued on Mar. 11, 1986. The patent application dominates most of the market.
The shortcomings of the SLA are:
a. establishing support;
b. because of liquid resins, the material buckets must be completely filled so that the material cost will be high.
2. SLS: illuminating the hi-molecule resin powders by hi-power laser to sinter and the resins are melted and affix to the work pieces to form a thin layer. After that, the Z-axis of the machine descends and a new layer of powder is spread on the work piece by using a scraper. The outer layer is then sintered by the laser beams. By repeating the procedures, an overall 3-D solid work piece is obtained. The SLS flow chart is shown in FIG. 3.
The typical problems of the SLS are:
a. the powder cannot be spread evenly by using rollers or scrapers;
b. the powder needs a long period of time to be warmed which prolongs the working hours;
c. the powder easily causes flaying dust and potentially harmful to human health.
d. the powder is difficult to be heated evenly;
e. unavailable for the production of large work pieces.
3. FDM: the powder of work piece is pre-mixed with binder to form elongate stripes, the stripes are heated and melted and using nozzles to feed for production. The main defect of this method is that the surface of work piece is rough and requires support. The flow chart is shown in FIG. 4.
4. 3DP: it is also known as 3-D printing. This method establish a thin layer of powder and selectively sprays adhesive on the surface of powder by method of jetting such that the powder is affixed and form a thin layer on solid work pieces. By repeating the procedures, we can finish the production of 3-D solid work piece. The flow chart (shown as FIG. 5) of 3DP includes the problems as below:
a. Due to the formation is fully depended upon nozzles, the precision of nozzles is high.
b. It will come with inferior precision.
c. The materials of work pieces can only be porous items.
d. The powder cannot be spread with uniform densities.
5. LOM: The already-solidified thin layers are cut to some cross-sectional slices by laser and the layers are connected by binder. By this method, the molecules within the material layers are well linked. Before production, each layer of material must be prepared individually, resulting in complex operation procedures. Furthermore, the largest defect of this process is that the removal of reside materials is quite difficult.
6. OBJet: OBJet is also a type of 3-D printing process. The OBJet is designed with 2 different types of materials. One type of the materials is the material to create the 3-D solid work pieces and the other type of material is used as support for the models of work pieces. With the OBJet method, the nozzles are filled with two different types of materials and then use the ultraviolet radiation to make maturity of the materials of work pieces and the strength will be also enhanced. The materials used as support finally becomes gel type substance. By repeating the foresaid procedures, we can finish the a 3-D solid work piece.
The OBJet production process is featured with the advantages like high quality, high precision, cleansing and speedy operation. However, within the production process, the most important component is the nozzle. If the nozzle control is inferior, the precision of finished products will be much more defective. The nozzle of high precision is quite expensive but results in frequent congestion and this situation will significantly affect to cause much production cost.
7. The conventional DLP (Radiation Hardening Formation): DLP is also a type of stereolithography process and the differences compared with SLA are that the SLA is meant to harden the resin by use of a laser. Because the laser beams are thin and liner laser beams, thus, it will prolong the production process. Also, the cost for using a laser as ignition resource is high. DLP (Radiation Hardening Formation) is radiated with the light radiated from halides and it is further controlled by DMD (Digital Micromirror Device) for the hardening radiation directly onto the resins. Because the light sources of DLP are able to illuminate a certain zone, it can significantly shorten the working hours. The DLP production process is controlled by DMD for precise processing. Currently, the resolution can reach 1280*1024; namely, the common difference can be reduced within+/−0.005 inch.
The DLP uses a single material. When the product is formed by means of DLP, the material is hardened by light illuminating. As the working platform is descended, the hardened materials is covered by a layer of unhardened materials. By repeating the foresaid procedures, we can finish a 3-D solid work piece. The major problems happening to DLP are:
1. Because of the preparation for fluid materials, the material bucket for work piece must be completely filled. Thus, it causes high material consumption and cost.
2. The precision is entirely controlled by DMD. Thus, the high precision of DMD is extremely required so that it will directly cause higher production cost.
3. The process is thoroughly triggered by light sources so that light isolation becomes critically important. Also, the DMD is available for provision of low density light and it is quite sensitive to the ambient light sources. Thus, the material buckets are also vulnerable for light reaction to cause the increasing difficulty for material storage.
4. When creating some work pieces, additional supports are required.
5. Due to the large illumination area, if the intensity of light sources is not high enough, the material cannot react as desired.
The processing flow chart of DLP is shown in FIG. 6 to 8.
Beside the seven types of technologies, hereby, another Rapid Prototype Methods proposed by Hwahsing Tang is introduced in 2001. This method is especially meant for the creation of 3-D ceramic work pieces. Firstly, the inorganic binder and dissolving agent will be added into the ceramic powder. These materials will be formed into a composite with plasticity. Thereafter, the composite will be placed with a thin layer and the layer is subsequently heated to harden the materials. At this moment, due to the moisture decrement of inorganic binders when it is hardened to cause higher density and affixation, it will result in slightly inferior intensity. As for the substance property, it acts like the dried slur from the sintered ceramic materials. Following that, laser beams are used to sinter the selected zone for the secondary hardening process. At this moment, the hardening is well affixed by the sintering of ceramic powder. The strength is far beyond the hardened parts merely through dehydration. Thus, the inventor can select an adequate method to separate the substances from the materials with two hardness degrees. However, this production process is mainly applied to the production of ceramic work pieces to perform the relevant ceramic slur technologies. It is actually not suitable for the rapid prototyping general work pieces.